Gets or sets a value specifying the source of complete strings used for automatic completion.
Use the AutoCompleteCustomSource, AutoCompleteMode, and AutoCompleteSource properties to create a ComboBox that
automatically completes input strings by comparing the prefix being
entered to the prefixes of all strings in a maintained source. This
is useful for ComboBox controls in which URLs, addresses, file
names, or commands will be frequently entered.
The use of the AutoCompleteCustomSource property is optional, but you must set the AutoCompleteSource property to CustomSource in order to use AutoCompleteCustomSource.